Relay



May 7, 1946. s. WALD 2,399,9oi

RELAY Filed Nov. 14, 1944 INVENTOR. SIDNEY WALD ATTORNEY of current.

Patented May 7, 1946 1 1 UNITED STATES PATENT orrlca I RELAY Sidney Wald, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application November 14, 1944, Serial No. 563,429 3 Claims. (01. 175-320) This invention relates to time delay relay and has for its object the'provision of an improved and compact relay which will operate only upon a 'prolonged departure from normal of the current in the circuit with which the relay is associated,

but which will not be operated by short surges Other objects of the invention include the provision of a. relay of the type indicated'in which the time delay is substantially independent of variations in temperature, altitude, pressure and vibration, which i widely adjustable and which will provide an indication of rapidly recurring surges of current in the circuit tobecontrolled. r

Various means have-hitherto been employed for procuring delay in the operation of a relay. In practice, magnetic means provide only short delays of the order of milliseconds. For larger delays, devices of the dashpot type are commonly employed; in these the relay does not operate until a fluid such as air, water or oil is forced through an orifice from one chamber into another. achieved by devices of this type is subject to change due to variations in temperature, pressure, altitude and vibration. To procure substantial delay it is necessary to make the delay relay devices large and massive, and for all these reasons they are highly unsuitable for use in equipment to be installed in aircraft.

The invention calls for the combination, with conventional elements of a relay,'of rotatable means and of means for providing mechanical inertia. These means may consist of an electric motor with a fly-wheel, the motor being of such a type and so connected that its speed is a function of current in the circuit to be controlled.

The motor provides a counter-electromotive force proportional to its speed and this electromotive force is employed to actuate the relay, adjustable delay being introduced by means of the fly-wheel.

An embodiment of the invention is illustrated by the accompanying drawing, the single figure of which is a schematic representation of a circuit which includes the relay of the invention.

In the drawing, a tube I is represented as having an anode l2 and a cathode l4. A circuit It connects these two electrodes, and it is this circuit which is to be controlled by the relay. The invention is, however, applicable to the control of any type of electrical circuit. The circuit in eludes an unbiased micro-switch l8, an electric motor 21 and a source of power, represented diagrammatically at 36, for the anode. The switch i normally closed, this being efiected manually Among other disadvantages, thedelay by setting it in the up position. Above the switch is an arm 30 pivoted at one end 32 and held away from the switch by a spring 34. Operation of the switch is controlledby a solenoid 20 and the enclosed magnetic core 22, as schematically represented in the drawing. Energization of the solenoid causes the core 22 to attract the arm 30 against the bias of the spring 34 and thus to open the switch l8 and, therefore, the circuit l6.

The motor 24 is provided with terminals 38 and is connected to the circuit l6 by means of these terminals. The motor is also connected by means of the same terminals and conductors 40 to the solenoid winding'lfl. Anode current inthe circuit l6 therefore divides, part fiOWing through the motor 24 and part through the solenoid 20. The

motor is of the type which has a permanent fleld magnet. The motor speed is proportional to current flowing in its energizing circuit, in this case the circuit Hi. In its rotation the motor armature generates a counter electromotive force,

which is proportional to the speed of the motor and which is impressed through the conductors 40 across the solenoid. The circuit elements are had a diameter of approximately one inch and a thickness of one-quarter inch.

The operation of the device is as follows: If current in circuit l6 increases, thetorque of the motor increases also. This torque is, however, opposed by the inertia of the fly-wheel. If the increase is sustained, the angular velocity of the motor armature and the fly-wheel increases slowly and the counter'electromotive force produced by the motor rises to a point sufficient to energize the solenoid; this, in turn, operates the microswitch and breaks the circuit 16. If, however, the increase of anode current is a surge of short duration this will not be sufilcient to increase the angular velocity of the motor armature and of the fly-wheel sufllciently to energize the solenoid, and the relay will not be actuated.

In the operation of a circuit, a series of surges of current may occur in rapid succession, each of these surgesbeing insumcient in itself to speed up the motor enough to actuate the relay. Each of the surges will, however, have increased the angular velocity of the fly-wheel to some extent, and if the period between recurrence of the surges is small so that the motor will not have had time to slow down to its normal running speed, then the cumulative efiect of the surges will be equivalent to a sustained increase of current and the relay will be actuated. v

The relay may be arranged to operate an alarm or other indicating device, instead of or in additon to being employed to break the circuit l8; or it may be arranged to perform any other operation according to methods oi. the prior art.

After the relay has been actuated and the cause of abnormal functioning of the circuit removed, the micro-switch may be manually reset. Alternatively, the switch may be biased bya spring, for example, and will then automatically reset itself when the speedof the motor armature and fly-wheel have been retarded suillciently to reduce the electromotive force across the solenoid. If the cause of abnormal functioning is not removed, the circuit will remain open, and the motor-will come to a standstill.

The switch i8 may include contacts 42 and 44 and a contact member 18, and the circuit elements may be so chosen in accordance with wellknown means of the prior art as to open the switch [8 and hence the circuit l6, when current in that circuit falls below normal as well as when it exceeds it.

By contrast with prior art means of procuring time delay in a relay, the delay achieved according to the invention, being dependent on the mass of the fly-wheel only, is independent of variations in temperature, altitude, pressure and vibration, and is widely adjustable. Adjustment may be efiected by adding weights to the fly-wheel or whose'speed of rotation is a function of current in the circuit to be controlled and which serves to provide an electromotive force to operate the relay.

I claim as my'invention:

l. A time delay relay which includes the combination of means having negligible inertia and continuously rotating at a speed dependent on current flowing in a circuit to be controlled by the relay, means having a predetermined inertia many times that of the said rotating means associated with said means and tending to retard any variation in the speed of rotation of the rotating means, and electromagnetic means responsive to a predetermined speedof rotation of the rotating means for performing an operation.

2. A time delay relay including in combination a switch, electromagnetic means disposed in operative relation to said switch and responsive to a current to be controlled by said relay, an electric motor, having a continuously rotating armature, energized by said current, the speed of the armature of said motor being a. function of said current and said armature having a negligible inertia, said motor being so connected as to apply its counter electromotive force to said electromagnetic means, and adjustable mechanical means having an inertia many times the inertia of said armature associated with said motor to retard any variation in the speed of said armature, whereby to delay any variation in said counter electromotive force and therefore to by substituting a fly-wheel of different mass from maintain the operation of said electromagnetic means substantiall independent of short surges of said current.

3. A time delay relay including in combination a switch, electromagnetic means disposed in operative relation to said switch and responsive to a current controlled by said relay, an electric motor, having a continuously rotating armature of negligible mass, energized by said current and connected to apply its counter electromotive force to said electromagnetic means, and a flywheel associated with said motor, said flywheel having a mass relatively large compared to the mass of said armature, whereby any variation in the speed of said armature is retarded and whereby any variation in said counter electromotive force is delayed.

SIDNEY WALD. 

